Conventionally, an optical semiconductor device including a light emitting diode (LED) described in the following PTL 1 has been known. The optical semiconductor device includes an LED which is a light emitting element and a molding to place the LED. The molding has a first lead electrically connected to one electrode of the LED and a second lead electrically connected to another electrode of the LED through wire. In addition, the molding has a concave portion with a bottom surface and lateral surfaces on which the LED is placed and a sealing member to seal the LED is filled into the concave portion. Because the molding has high reflectance, transmittance of light for the lateral surfaces and the bottom surface of the concave portion decreases and the light is efficiently emitted from the LED.